The old pump in your tractor starts to whine and lose power. So you buy a brand new one, remove the old one (noticing some metal shavings at the bottom of the tank in the process), install the new one, and refill it with the old, but "still pretty and clear," oil.
For the first few weeks, the machine works like a charm. Unfortunately, after a month, the problem returns. The pump whines again, and the loader drops. You call the store, furious that they sold you a "Chinese piece of junk," and demand a warranty replacement. The manufacturer disassembles the pump, rejects your claim, and you're left with nothing. What went wrong?
BRhydraulic experts explain why old oil acts like liquid sandpaper and how proper filtration saves your money.
1. The illusion of "clean" oil
The biggest mistake in hydraulic power is judging oil cleanliness "by eye." Just because the oil is clear and has a nice, straw color doesn't mean it's clean at all!
Components inside gear pumps, piston pumps, or modern directional control valves are fitted to fractions of a millimeter (so-called microns). The human eye can only see dirt particles from about 40 microns in size. However, the most dangerous for the pump are hard metal shavings and contaminants with a size of 5-15 microns. Circulating in the system under 200 bar pressure, these microscopic particles act like sandblasting, literally eroding the new pump from the inside in a few weeks.
2. Clogged suction filter and deadly cavitation
Let's look into the oil tank. On the pipe that sucks oil into the pump, there is usually a steel mesh – a suction filter. What happens when you forget about it and it gets covered in dirt?
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Pump starvation: The pump tries to suck in thick oil, but the clogged filter creates enormous resistance. A vacuum is formed.
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Cavitation: Due to the vacuum, air bubbles begin to separate from the oil (the oil starts to "boil" cold). When these bubbles reach the discharge side of the pump (where there is 200 bar), they violently implode (collapse into themselves).
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Result: These mini-explosions have such enormous force that they tear out microscopic pieces of cast iron or aluminum from inside the pump casing. The pump starts to whine terribly loudly and destroys itself in a short time.
3. Three lines of defense: Where to install filters?
For the system to last for years, it must be protected in appropriate sections. A simple "mesh" in the tank is not enough.
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Suction filter (in the tank): Protects the pump from sucking in large elements (e.g., a broken spring, Teflon pieces, nuts). Always check that it is not clogged with sludge!
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Return filter (most important!): Mounted on the hose or tank housing, just before the oil returns. Oil returning from cylinders (collecting dirt from seals and wearing gears) passes through a precise fiberglass or paper element (often 10-25 microns) before returning to the tank. This is an absolute must-have for every machine.
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Pressure filter (for professionals): Mounted on the high-pressure line (immediately after the pump). It is used in forestry and construction machines, where damage to a powerful pump would scatter metal shavings directly into extremely expensive and sensitive proportional directional control valves.
Summary
Replacing just the pump without flushing the system and installing new filters is like putting on new, white socks on dirty feet – the effect will last for a very short time. Saving a few dozen zlotys on a filter element usually ends in a breakdown costing thousands. Take care of your system's "kidneys," and it will repay you with many years of trouble-free operation!
